Image forming apparatus and light guide member

ABSTRACT

A light guide member has a transmitting/reflecting portion transmitting and reflecting light that is emitted from a light source, to enter one end of the light guide member in a longitudinal direction, and be guided to the other end of the light guide member so that the light is applied to: a position between the developing roller and the transfer roller on the image carrier on a downstream side in the traveling direction of the transfer target member; and a position between the transfer roller and the cleaning portion on the image carrier on an upstream side in the traveling direction of the transfer target member. Furthermore, the light guide member has a convex portion having an arc-shaped cross section and being formed outward at a position opposing the transmitting/reflecting portion in a part of a predetermined specific region at one end or both ends in the longitudinal direction.

INCORPORATION BY REFERENCE

This application is based upon and claims the benefit of priority fromthe corresponding Japanese Patent Application No. 2014-236153 filed onNov. 21, 2014, the entire contents of which are incorporated herein byreference.

BACKGROUND

The present disclosure relates to an electrophotographic image formingapparatus and a light guide member used in the electrophotographic imageforming apparatus.

In an electrophotographic image forming apparatus, a photosensitive drumis uniformly charged by a charging roller. Next, laser light is appliedto a surface of the charged photosensitive drum, and thus anelectrostatic latent image is formed on the surface of thephotosensitive drum. Then, the electrostatic latent image on thephotosensitive drum is developed by using toner. Then, after the tonerimage on the photosensitive drum is transferred onto a transfer targetmember such as a sheet or an intermediate transfer belt, thephotosensitive drum is discharged by discharging light emitted from adischarging portion, and the surface of the photosensitive drum iscleaned by a cleaning portion.

In some cases, a discharging portion, which applies discharging light tothe photosensitive drum before transfer of the toner image on thephotosensitive drum onto the transfer target member, is provided.Furthermore, an arrangement is known in which light emitted from a lightsource is reflected, by a light guide member having two reflectionsurfaces, toward: a position at which a toner image has been transferredand which is a position of a photosensitive drum on an upstream side ina traveling direction of the transfer target member; and a position atwhich a toner image has not been transferred and which is a position ofa photosensitive drum on a downstream side in the traveling direction ofthe transfer target member.

SUMMARY

An image forming apparatus according to one aspect of the presentdisclosure includes: a plurality of image carriers; a developing roller;a transfer roller; a cleaning portion; a light source; and a light guidemember. The image carriers are arranged along a traveling direction of atransfer target member. The developing roller develops an electrostaticlatent image formed on each image carrier as an toner image. Thetransfer roller transfers the toner image formed on each image carrieronto the transfer target member. The cleaning portion cleans each imagecarrier after the toner image is transferred onto the transfer targetmember by the transfer roller. The light source emits light used todischarge each image carrier. The light guide member has atransmitting/reflecting portion transmitting and reflecting light thatis emitted from the light source, to enter one end of the light guidemember in a longitudinal direction, and be guided to the other end ofthe light guide member so that the light is applied to: a positionbetween the developing roller and the transfer roller on the imagecarrier on a downstream side in the traveling direction of the transfertarget member; and a position between the transfer roller and thecleaning portion on the image carrier on an upstream side in thetraveling direction of the transfer target member. Furthermore, thelight guide member has a convex portion having an arc-shaped crosssection and being formed outward at a position opposing thetransmitting/reflecting portion in a part of a predetermined specificregion at one end or both ends in the longitudinal direction.

A light guide member according to another aspect of the presentdisclosure is an elongated member used in an image forming apparatusincluding: a plurality of image carriers arranged along a travelingdirection of a transfer target member; a developing roller configured todevelop an electrostatic latent image formed on each image carrier as atoner image; a transfer roller configured to transfer the toner imageformed on each image carrier onto the transfer target member; a cleaningportion configured to clean each image carrier after the toner image istransferred onto the transfer target member by the transfer roller; anda light source configured to emit light used to discharge each imagecarrier. The light guide member has a transmitting/reflecting portionand a convex portion, the transmitting/reflecting portion transmittingand reflecting light that is emitted from the light source, to enter oneend of the light guide member in a longitudinal direction, and be guidedto the other end of the light guide member so that the light is appliedto: a position between the developing roller and the transfer roller onthe image carrier on a downstream side in the traveling direction of thetransfer target member; and a position between the transfer roller andthe cleaning portion on the image carrier on an upstream side in thetraveling direction of the transfer target member, the convex portionhaving an arc-shaped cross section and being formed outward at aposition opposing the transmitting/reflecting portion in a part of apredetermined specific region at one end or both ends in thelongitudinal direction.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription with reference where appropriate to the accompanyingdrawings. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter. Furthermore,the claimed subject matter is not limited to implementations that solveany or all disadvantages noted in any part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a configuration of an image formingapparatus according to an embodiment of the present disclosure.

FIG. 2 is a diagram illustrating an example of image forming units ofthe image forming apparatus illustrated in FIG. 1.

FIG. 3 is a diagram illustrating a discharging portion of the imageforming unit illustrated in FIG. 2.

FIG. 4 is a diagram illustrating a light guide member of the dischargingportion illustrated in FIG. 3.

DETAILED DESCRIPTION

Hereinafter, for understanding of the present disclosure, an embodimentof the present disclosure will be described based on the drawings. Notethat the embodiment below is a specific exampe of the present disclosureand does not limit the technical scope of the present disclosure.

As iustrated in FIG. 1, an image forming apparatus 10 includes aplurality of image forming units 1 to 4, an intermediate transfer belt5, a laser scanning unit 6, a secondary transfer roller 7, a fixingdevice 8, a sheet discharge tray 9, toner containers 21 to 24, a sheetfeeding cassette 31, and a conveyance path 32. The image formingapparatus 10 is a color printer that forms a color image or a monochromeimage based on image data inputted from an information processingapparatus such as a personal computer on a sheet supplied along theconveyance path 32 from the sheet feeding cassette 31.

The image forming units 1 to 4 are arranged along a traveling directionD1 of the intermediate transfer belt 5 and constitute a so-called tandemtype image forming portion. Specifically, the image forming unit 1 formsa Y (yellow) toner image, the image forming unit 2 forms an M (magenta)toner image, the image forming unit 3 forms a C (cyan) toner image, andthe image forming unit 4 forms a K (black) toner image. In the presentembodiment, the intermediate transfer belt 5 is described as an exampleof a transfer target member, but a sheet such as a printing sheet may bean example of a transfer target member. That is, an arrangement in whicha toner image is transferred onto a sheet conveyed by a sheet conveyorbelt is possible as another embodiment.

As illustrated in FIG. 2, the image forming unit 1 and the image formingunit 2 are electrophotographic image forming units each including aphotosensitive drum 11, and a charging portion 12, a developing portion13, a discharging portion 14, a primary transfer roller 15, and acleaning device 16 that correspond to the photosensitive drum 11. Notethat the image forming unit 3 and the image forming unit 4 have asimilar configuration, and therefore description thereof is omitted.

Each of the photosensitive drums 11 is arranged along the travelingdirection of the intermediate transfer belt 5 and is an image carrierthat carries an electrostatic latent image and a toner image. Each ofthe charging portions 12 has a charging roller 121 that charges thephotosensitive drum 11 by electric power supplied from a power source(not shown). Next, laser light by the laser scanning unit 6 is appliedto the photosensitive drum 11 charged by the charging portion 12, andthus an electrostatic latent image based on image data is formed on anouter peripheral surface of the photosensitive drum 11. Each of thedeveloping portions 13 has a developing roller 131 that develops theelectrostatic latent image formed on the photosensitive drum 11 by usingtoner (developer). Note that an external additive such as a lubricatingagent or a polishing agent is used together with toner to develop theelectrostatic latent image by the developing portion 13. Toner issupplied from the detachable toner containers 21 to 24 corresponding tothe respective colors to the respective developing portions 13.

Each of the primary transfer rollers 15 transfers the toner image formedon the photosensitive drum 11 onto the intermediate transfer belt 5. Theintermediate transfer belt 5 is an intermediate transfer member thattravels on the photosensitive drums 11 of the respective image formingunits 1 to 4 and on which toner images of the respective colors formedon the respective photosensitive drums 11 are sequentially transferredso as to overlap each other. Then, the toner image on the intermediatetransfer belts 5 is transferred onto a sheet conveyed via the conveyancepath 32 from the sheet feeding cassette 31 by the secondary transferroller 7. Then, the toner image transferred onto the sheet is heated bythe fixing device 8 so as to be fused and fixed on the sheet. Each ofthe cleaning devices 16 has a cleaning portion 161 such as a cleaningroller or a cleaning blade that cleans the photosensitive drum 11 afterthe toner image is transferred onto the intermediate transfer belt 5 bythe primary transfer roller 15.

Each of the discharging portions 14 applies discharging light L1 fordischarging the photosensitive drum 11 to a position between the primarytransfer roller 15 and the cleaning portion 161 on an outer peripheralsurface of the photosensitive drum 11 on an upstream side of thetraveling direction D1 of the intermediate transfer belt 5. In otherwords, each of the discharging portions 14 applies the discharging lightL1 to a position that is, in a rotation direction of the photosensitivedrum 11, on a downstream side of the primary transfer roller 15 and onan upstream side of the cleaning portion 161. Furthermore, each of thedischarging portions 14 applies discharging light L2 for discharging thephotosensitive drum 11 to a position between the developing roller 131and the primary transfer roller 15 on an outer peripheral surface of thephotosensitive drum 11 on a downstream side of the traveling directionD1 of the intermediate transfer belt 5. In other words, each of thedischarging portions 14 applies the discharging light L2 to a positionthat is, in the rotation direction of the photosensitive drum 11, on adownstream side of the developing roller 131 and on an upstream side ofthe primary transfer roller 15. A so-called memory image of thephotosensitive drum 11 is suppressed by discharging the photosensitivedrum 11 before and after transfer of the toner image of thephotosensitive drum 11 onto the intermediate transfer belt 5.

Since a yellow image is not noticeable, the problem of occurrence of animage memory hardly become evident even if the discharging light L2 isnot applied to the photosensitive drum 11 of the image forming unit 1that corresponds to yellow. Therefore, in the image forming apparatus10, a discharging portion 14 that applies discharging light L2 to thephotosensitive drum 11 of the image forming unit 1 is omitted. That is,in the image forming apparatus 10, the photosensitive drum 11 disposedon the most upstream side of the traveling direction D1 is one thatcorresponds to yellow, and the discharging portion 14 including a lightsource 141 and a light guide member 142 is disposed only at positions onthe downstream side of the respective photosensitive drums 11 in thetraveling direction D1. Needless to say, it is possible to employ anarrangement in which the image forming apparatus 10 includes adischarging portion 14 that applies the discharging light L2 to thephotosensitive drum 11 of the image forming unit 1.

Next, the discharging portion 14 is described with reference to FIGS. 3and 4.

The discharging portion 14 is disposed between the photosensitive drum11 disposed on the upstream side in the traveling direction D1 of theintermediate transfer belt 5 and the photosensitive drum 11 disposed onthe downstream side in the traveling direction D1 of the intermediatetransfer belt 5. The discharging portion 14 has the light source 141 andthe light guide member 142 elongated in an axial direction D2 of thephotosensitive drum 11. The light guide member 142 is longer than thephotosensitive drum 11, and the longitudinal direction of the lightguide member 142 is parallel with the axial direction D2 of thephotosensitive drum 11.

The light source 141 is, for example, an LED light source that emitslight for discharging the photosensitive drum 11. The light emitted fromthe light source 141 enters a light incident surface 143 formed at oneend of the light guide member 142 in the longitudinal direction. In thelight guide member 142, the light that enters from the one end at whichthe light incident surface 143 is formed is guided toward an end surface144 at the other end while being repeatedly reflected. In the presentembodiment, a case where the light source 141 is provided at one end ofthe light guide member 142 is described as an example. However, anarrangement in which the light source 141 is provided at both ends ofthe light guide member 142 and light enters from both of the lightincident surface 143 and the end surface 144 is also possible as anotherembodiment.

The light guide member 142 is a substantially cylindrical shaped memberwhose cross section has a D-shape (semicircular shape) and that has aflat surface 145 and a curved surface 146 and is, for example, made of amaterial such as a resin.

A plurality of transmitting/reflecting portions 147 are formed on theflat surface 145 at predetermined intervals in the longitudinaldirection.

Specifically, the transmitting/reflecting portions 147 are inclinedsurfaces formed inwardly from the flat surface 145 at a predeterminedinclination angle. The inclination angle of the transmitting/reflectingportions 147 is appropriately determined so that the amount oftransmission and the amount of reflection of the light emitted from thelight source 141 in the transmitting/reflecting portions 147 have apredetermined relationship. For example, the inclination angle of thetransmitting/reflecting portions 147 is determined so that a ratio ofthe amount of discharging light L1 that reaches the photosensitive drum11 on the upstream side in the traveling direction D1 of theintermediate transfer belt 5 and the amount of discharging light L2 thatreaches the photosensitive drum 11 on the downstream side in thetraveling direction D1 of the intermediate transfer belt 5 becomes 1:10.

In the discharging portion 14, the light emitted from the light source141 is reflected by the transmitting/reflecting portions 147. Thiscauses the light to be applied as the discharging light L1 fordischarging the photosensitive drum 11 to the position between theprimary transfer roller 15 and the cleaning device 16 on the outerperipheral surface of the photosensitive drum 11 on the upstream side inthe traveling direction D1 of the intermediate transfer belt 5.

In the discharging portion 14, the light emitted from the light source141 passes through the transmitting/reflecting portions 147. This causesthe light to be applied as the discharging light L2 for discharging thephotosensitive drum 11 to the position between the developing roller 131and the primary transfer roller 15 on the outer peripheral surface ofthe photosensitive drum 11 on the downstream side in the travelingdirection D1 of the intermediate transfer belt 5.

Meanwhile, the arrangement in which a light guide member has tworeflection surfaces as in the related art described above has a problemthat the shape of a metal mold for formaion of the light guide memberbecomes complicated. However, the image forming apparatus 10 makes itpossible to simplify the shape of a metal mold for molding the lightguide member 142 since only the one flat surface 145 having thetransmitting/reflecting portions 147 is formed in the light guide member142.

Note that the light guide member 142 may be roated by 180 degrees. Thatis, the discharging portion 14 may be arranged such that the lightemitted from the light source 141 is reflected by thetransmitting/reflecting portions 147 so as to be applied as thedischarging light L2 to the position between the developing roller 131and the primary transfer roller 15 on the outer peripheral surface ofthe photosensitive drum 11 on the downstream side in the travelingdirection D1 of the intermediate transfer belt 5. In this case, thedischarging portion 14 is arranged such that the light emitted from thelight source 141 passes through the transmitting/reflecting portions 147so as to be applied as the discharging light L1 to the position betweenthe primary transfer roller 15 and the cleaning device 16 on the outerperipheral surface of the photosensitive drum 11 on the upstream side inthe traveling direction D1 of the intermediate transfer belt 5.

In the light guide member 142, the amount of light gradually declineswhile the light incident from the light source 141 is guided from oneend to the other end. Accordingly, in the light guide member 142,intervals P1 at which the transmitting/reflecting portions 147 areformed in the longitudinal direction become shorter as the distance fromthe light source 141 becomes longer. This increases the amount ofreflection and the amount of transmission of the light by thetransmitting/reflecting portions 147 at positions far from the lightincident surface 143 of the light guide member 142, thereby achievinguniformity of the discharging light L1 and the discharging light L2 inthe longitudinal direction of the light guide member 142. Furthermore,an arrangement in which the sizes of the transmitting/reflectingportions 147 become larger as the distance from the light source 141becomes longer may be employed as an arrangement for achievinguniformity of the discharging light L1 and the discharging light L2emitted from the light guide member 142.

In a case where the amount of discharging light that is applied from thevicinity of the end of the light guide member 142 on the light source141 side to an image formation region A1 of the photosensitive drum 11on the downstream side in the traveling direction D1 of the intermediatetransfer belt 5 is insufficient, there is a risk of inhibitinguniformity of the discharging light. Specifically, in the light guidemember 142, the discharging light L2 that has passed through thetransmitting/reflecting portions 147 is applied to the photosensitivedrum 11 at a certain angle. This may undesirably cause the amount oflight to be applied to an end portion of the image formation region A1of the photosensitive drum 11 to be smaller than that in the otherregion.

Furthermore, in a case where discharging light of a high intensity isapplied from the vicinity of the end of the light guide member 142 onthe light source 141 side to the image formation region A1 of thephotosensitive drum 11 on the upstream side in the traveling directionD1, there is a risk of inhibiting uniformity of the discharging light.Specifically, in a case where light of a high intensity is applied froma position in the vicinity of the light source 141 on the curved surface146 of the light guide member 142 and reaches the image formation regionA1 of the photosensitive drum 11 on the upstream side in the travelingdirection D1 of the intermediate transfer belt 5, there is a risk ofinhibiting uniformity of the amount of discharge of the image formationregion A1.

In view of this, the light guide member 142 has a light diffusingportion 148 at a position corresponding to a non-image formation regionA2 that is outside of the image formation region A1 of thephotosensitive drum 11. The light diffusing portion 148 is a convexportion having an arc-shaped cross section and being formed outward, andis formed on the opposing the transmitting/reflecting portions 147 in apart of a predetermined specific region corresponding to the non-imageformation region A2 at one end or both ends of the light guide member142 in the longitudinal direction. For example, the light diffusingportion 148 has a hemispherical shape. The light diffusing portion 148may have a shape obtained by cutting a part of a sphere or a spheroid.

With the arrangement, light reflected by the light diffusing portion 148of the light guide member 142 is applied as the discharging light L2from the flat surface 145 to the end of the image formation region A1 ofthe photosensitive drum 11 on the downstream side in the travelingdirection D1 of the intermediate transfer belt 5. It is thereforepossible to compensate for the insufficiency of the amount of light atthe end of the image formation region A1 of the photosensitive drum 11on the downstream side in the traveling direction D1 of the intermediatetransfer belt 5, thereby uniforming the amount of discharge.

Furthermore, since light that passes through the curved surface 146 fromthe light guide member 142 is diffused by the light diffusing portion148, the amount of light that reaches, as the discharging light L1, theimage formation region A2 of the photosensitive drum 11 on the upstreamside of the traveling direction D1 in the intermediate transfer belt 5is suppressed. It is therefore possible to uniform the amount ofdischarging light applied to the image formation region A1 of thephotosensitive drum 11 on the upstream side in the traveling directionD1 of the intermediate transfer belt 5.

As illustrated in FIG. 2, a transparent or semi-transparentlight-transmitting member 17 is provided as a cover member that covers apart or the entirety of the light source 141 and the light guide member142 of the discharging portion 14. This prevents dust or toner fromattaching to the light source 141 and the light guide member 142 of thedischarging portion 14, thereby making it possible to prolong the lifetime of the image forming apparatus 10.

It is to be understood that the embodiments herein are illustrative andnot restrictive, since the scope of the disclosure is defined by theappended claims rather than by the description preceding them, and allchanges that fall within metes and bounds of the claims, or equivalenceof such metes and bounds thereof are therefore intended to be embracedby the claims.

The invention claimed is:
 1. An image forming apparatus comprising: aplurality of image carriers arranged along a traveling direction of atransfer target member; a developing roller configured to develop anelectrostatic latent image formed on each image carrier as a tonerimage; a transfer roller configured to transfer the toner image formedon each image carrier onto the transfer target member; a cleaningportion configured to clean each image carrier after the toner image istransferred onto the transfer target member by the transfer roller; alight source configured to emit light used to discharge each imagecarrier; and an elongated light guide member having atransmitting/reflecting portion and a convex portion, thetransmitting/reflecting portion transmitting and reflecting light thatis emitted from the light source, to enter one end of the light guidemember in a longitudinal direction, and be guided to the other end ofthe light guide member so that the light is applied to: a positionbetween the developing roller and the transfer roller on the imagecarrier on a downstream side in the traveling direction of the transfertarget member; and a position between the transfer roller and thecleaning portion on the image carrier on an upstream side in thetraveling direction of the transfer target member, the convex portionhaving an arc-shaped cross section and being formed outward at aposition opposing the transmitting/reflecting portion in a part of apredetermined specific region at one end or both ends in thelongitudinal direction, wherein the light guide member is an elongatedmember that has one flat surface having a plurality of thetransmitting/reflecting portions.
 2. The image forming apparatusaccording to claim 1, wherein the specific region is a region thatcorresponds to a non-image formation region of the image carrier.
 3. Theimage forming apparatus according to claim 1, wherein the light guidemember is an elongated member that has one flat surface having aplurality of the transmitting/reflecting portions formed along thelongitudinal direction at predetermined intervals.
 4. The image formingapparatus according to claim 3, wherein the transmitting/reflectingportions are inclined surfaces that are formed inwardly from the flatsurface at a predetermined inclination angle.
 5. The image formingapparatus according to claim 3, wherein the intervals of thetransmitting/reflecting portions become shorter as a distance from thelight source becomes longer.
 6. The image forming apparatus according toclaim 3, wherein the sizes of the transmitting/reflecting portionsbecome larger as a distance from the light source becomes longer.
 7. Theimage forming apparatus according to claim 1, further comprising alight-transmitting member that covers a part or the entirety of an outerperiphery of the light guide member.
 8. The image forming apparatusaccording to claim 1, wherein the image carrier disposed on a mostupstream side in the traveling direction is an image carrier for yellow;and the light source and the light guide member are disposed only atpositions on a downstream side of each image carrier in the travelingdirection.
 9. An elongated light guide member used in an image formingapparatus including: a plurality of image carriers arranged along atraveling direction of a transfer target member; a developing rollerconfigured to develop an electrostatic latent image formed on each imagecarrier as a toner image; a transfer roller configured to transfer thetoner image formed on each image carrier onto the transfer targetmember; a cleaning portion configured to clean each image carrier afterthe toner image is transferred onto the transfer target member by thetransfer roller; and a light source configured to emit light used todischarge each image carrier, the light guide member having atransmitting/reflecting portion and a convex portion, thetransmitting/reflecting portion transmitting and reflecting light thatis emitted from the light source, to enter one end of the light guidemember in a longitudinal direction, and be guided to the other end ofthe light guide member so that the light is applied to: a positionbetween the developing roller and the transfer roller on the imagecarrier on a downstream side in the traveling direction of the transfertarget member; and a position between the transfer roller and thecleaning portion on the image carrier on an upstream side in thetraveling direction of the transfer target member, the convex portionhaving an arc-shaped cross section and being formed outward at aposition opposing the transmitting/reflecting portion in a part of apredetermined specific region at one end or both ends in thelongitudinal direction, the light guide member being an elongated memberthat has having one flat surface having with a plurality of thetransmitting/reflecting portions.
 10. An image forming apparatuscomprising: a plurality of image carriers arranged along a travelingdirection of a transfer target member; a developing roller configured todevelop an electrostatic latent image formed on each image carrier as atoner image; a transfer roller configured to transfer the toner imageformed on each image carrier onto the transfer target member; a cleaningportion configured to clean each image carrier after the toner image istransferred onto the transfer target member by the transfer roller; alight source configured to emit light used to discharge each imagecarrier; and an elongated light guide member having atransmitting/reflecting portion, the transmitting/reflecting portiontransmitting and reflecting light that is emitted from the light source,to enter one end of the light guide member in a longitudinal direction,and be guided to the other end of the light guide member so that thelight is applied to: a position between the developing roller and thetransfer roller on the image carrier on a downstream side in thetraveling direction of the transfer target member; and a positionbetween the transfer roller and the cleaning portion on the imagecarrier on an upstream side in the traveling direction of the transfertarget member, wherein the light guide member has one flat surfacehaving a plurality of the transmitting/reflecting portions.
 11. Anelongated light guide member used in an image forming apparatusincluding: a plurality of image carriers arranged along a travelingdirection of a transfer target member; a developing roller configured todevelop an electrostatic latent image formed on each image carrier as atoner image; a transfer roller configured to transfer the toner imageformed on each image carrier onto the transfer target member; a cleaningportion configured to clean each image carrier after the toner image istransferred onto the transfer target member by the transfer roller; anda light source configured to emit light used to discharge each imagecarrier, the light guide member having a transmitting/reflectingportion, the transmitting/reflecting portion transmitting and reflectinglight that is emitted from the light source, to enter one end of thelight guide member in a longitudinal direction, and be guided to theother end of the light guide member so that the light is applied to: aposition between the developing roller and the transfer roller on theimage carrier on a downstream side in the traveling direction of thetransfer target member; and a position between the transfer roller andthe cleaning portion on the image carrier on an upstream side in thetraveling direction of the transfer target member, the light guidemember having one flat surface with a plurality of thetransmitting/reflecting portions.
 12. An image forming unit comprising:a first image carrier; a developing roller configured to develop anelectrostatic latent image formed on the first image carrier as a tonerimage; a first transfer roller configured to transfer the toner imageformed on the first image carrier onto a transfer target member; acleaning portion configured to clean the first image carrier after thetoner image is transferred onto the transfer target member by the firsttransfer roller; a light source configured to emit light used todischarge the first image carrier; and an elongated light guide memberhaving a transmitting/reflecting portion, the transmitting/reflectingportion transmitting and reflecting light that is emitted from the lightsource, to enter one end of the light guide member in a longitudinaldirection, and be guided to the other end of the light guide member sothat the light is applied to: a position between the developing rollerand the first transfer roller on the first image carrier; and a positionbetween a second transfer roller and a second cleaning portion on asecond image carrier of another image forming unit disposed on anupstream side in a traveling direction of the transfer target member,the light guide member having one flat surface with a plurality of thetransmitting/reflecting portions.